LONDON, Aug 5 (Reuters) - Britain's long-running political civil war over Europe is as much about symbols as it is about substance.

So advisers to Prime Minister David Cameron are looking for one or two symbolic trophies he can claim in a renegotiation of the European Union's treaty before he asks Britons to support continued membership in a referendum promised for 2017.

According to a source familiar with the Conservative leader's thinking, London wants to erase or amend the goal of an "ever closer union" that has featured in the preamble of EU treaties since the founding 1957 Treaty of Rome.

To many Britons, those three words stand for an inexorable one-way journey in which national sovereignty ebbs to Brussels and the undeclared final destination is a European super-state.

"Ever closer union" has long been a red rag to John Bull, the patriotic cartoon Englishman draped in a Union Jack flag who feels his country signed up to a common market in 1973 but has become entangled in ever more intrusive European governance.

"We understand and respect the right of others to maintain their commitment to this goal. But for Britain - and perhaps for others - it is not the objective," Cameron said in January.

His aides are hoping to airbrush out the offending phrase or make clear it applies only to those, notably in the euro area, who want to pursue deeper integration.

Former French President Nicolas Sarkozy scored just such a semantic victory in 2007 when he had the term "free and unfettered competition" deleted from the EU's core values in the Lisbon Treaty. It changed nothing in European competition law.

Another symbol in London's sights is the concept of "European citizenship", established by the 1992 Maastricht Treaty. To British sovereignists (and Foreign Office lawyers), Europeans are citizens of their nation state, not of the EU.

BACK TO BLACK PASSPORTS?

In practice, "European citizenship" confers few rights, other than an entitlement for long-term EU residents of another member state to vote in local and European Parliament elections in that country.

But it means that Britons carry burgundy-coloured passports like other EU nationals with the words European Union embossed on the cover above the United Kingdom of Great Britain and Northern Ireland and the royal coat of arms.

The source said a return to the traditional black British passport without the offending EU moniker could be another symbolic win for Cameron.

Foreign Secretary William Hague pointed to some of the main areas where Britain wants change in the substance of EU law in a speech in Berlin in May, especially in social legislation.

Britons could not understand "why Brussels has to interfere in how long junior doctors can work or why someone from another Member State should be able to continue to claim benefits in the UK even after they have moved back to their own country," he said.

British regulations restricting EU migrants' welfare access has got London into legal trouble with the European Commission.

Scrapping or loosening EU rules that limit the work week to 48 hours, guarantee employees 11 hours of rest in any 24-hour period, and give temporary agency workers the same rights as permanent staff, are high priorities, British officials say.

Several other EU states, notably among the central and east European countries that joined the bloc in the last decade, also want to modify the work time legislation.

But for core countries of western Europe such as France and Germany, those rules are among the few social achievements that balance out the EU's business-friendly economic agenda.

"Social Europe is dead," the source close to Cameron said. "People in Europe believe Britain killed it with the eastern enlargement, and in a way we did by bringing in those east European countries who made it a race to the bottom."

Cameron says he also wants to complete the single market, cut down EU bureaucracy and increase the role of national parliaments. But he is unlikely to press old ambitions to prune the EU's Common Agricultural Policy, and he faces resistance from partners irked by British "cherry picking" of EU policies.

SENSITIVE

In a gesture to Eurosceptical Conservative lawmakers, the government announced last year it would opt out of more than 130 EU law-and-order cooperation measures under the Lisbon Treaty.

With less fanfare, it quietly asked last month to opt back in to 35 of those provisions, including the European Arrest Warrant, which allows the transfer of suspects between member states without lengthy extradition procedures.

A French government source said Deputy Prime Minister Nick Clegg of the pro-European Liberal Democrats, junior partners in Cameron's coalition, telephoned French Prime Minister Jean-Marc Ayrault to seek his support for letting Britain pick and choose which measures to rejoin.

"Clegg explained this was a very sensitive domestic issue and Cameron had only wanted to return to seven or eight areas, but he had fought to keep Britain in more," the source said.

Just how sensitive the European debate is was illustrated by the way the government slipped out the first three of a series of fact-finding reports on how EU membership affects Britain.

It waited until parliament was in recess and released the weighty studies without a news conference or an accompanying political summary on the day a royal baby was born.

Pro-Europeans hailed the core finding that the British economy benefits substantially from membership of the EU's single market while Eurosceptical newspapers chose to highlight the steep cost of European regulation for British business.

Some critics of EU membership said the studies missed the real point: the loss of national sovereignty which they regard as more important than economic arguments.

Nigel Farage, the leader of the UK Independence Party which has attracted many Conservative voters by campaigning for a British exit from the EU, dismissed the review as "a cynical and futile PR exercise".

That contest between cost-benefit analysis and ideological fundamentals prefigures a fierce and uncertain referendum campaign if the Conservatives win a 2015 general election.

"S/he who frames the case wins the argument on the EU," wrote British political blogger Jon Worth. (www.jonworth.eu)

In his quest for EU treaty change he can sell to voters, Cameron is betting on support from German Chancellor Angela Merkel because Berlin values Britain's free-marketeering role in balancing out French interventionism and trade protectionism.

"Germany is afraid of getting into bed in a ménage a deux with France," the source close to the prime minister said.

But he acknowledged that even if Britain secures changes in symbols and substance, a vote to stay in the EU is far from assured, not least because "Yes" campaigners could easily be depicted as a cosmopolitan elite, out of touch with the people. (Additional reporting by Guy Faulconbridge; Editing by Ruth Pitchford)